U.S. patent number 5,583,644 [Application Number 08/172,106] was granted by the patent office on 1996-12-10 for system for correcting image density of an image forming system based on a detection result of a test image.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Tetsuya Atsumi, Hisashi Fukushima, Nobuatsu Sasanuma.
United States Patent |
5,583,644 |
Sasanuma , et al. |
December 10, 1996 |
System for correcting image density of an image forming system
based on a detection result of a test image
Abstract
An image forming system includes a generator for generating an
image signal representing a predetermined test image having a
plurality of tone levels, an image forming device for forming the
predetermined test image on a recording medium based on the signal,
a first measuring device for measuring density levels of the formed
predetermined test image, corresponding to each of the plurality of
tone levels of the image signal, a controller for determining
characteristics of a change of density levels in the predetermined
test image to a change of tone levels in the image signal based on
a plurality of density levels measured by the first measuring
device, and for making a conversion data table for converting tone
levels of an input image signal in accordance with the
characteristics, a designator for generating instructions for
designation a correction of the conversion data table, a
transferring device for transferring the image formed on the
recording medium to a recording sheet, a second measuring device
for measuring density levels of the image on the recording sheet,
wherein the controller controls the generator, the image forming
device, and the transferring devices to correct the conversion data
table based on the density levels measured by the second measuring
device.
Inventors: |
Sasanuma; Nobuatsu (Yokohama,
JP), Fukushima; Hisashi (Kawasaki, JP),
Atsumi; Tetsuya (Tokyo, JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
|
Family
ID: |
18405127 |
Appl.
No.: |
08/172,106 |
Filed: |
December 23, 1993 |
Foreign Application Priority Data
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Dec 28, 1992 [JP] |
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4-349643 |
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Current U.S.
Class: |
358/296; 358/300;
358/406; 358/504; 358/519; 358/523; 399/72 |
Current CPC
Class: |
G03G
15/5062 (20130101); H04N 1/4078 (20130101); G03G
15/5041 (20130101); G03G 2215/00042 (20130101) |
Current International
Class: |
G03G
15/00 (20060101); H04N 1/407 (20060101); H04N
001/00 (); H04N 001/29 (); H04N 001/46 (); G03F
003/08 (); G03G 021/00 () |
Field of
Search: |
;358/296,298,300,406,474,504,505,519,523,524
;355/203,204,207,208,210,214 ;382/319 ;347/131,133,188,189 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0266186 |
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May 1988 |
|
EP |
|
4-268873 |
|
Sep 1992 |
|
JP |
|
Primary Examiner: Wong; Peter S.
Assistant Examiner: Frahm; Eric
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. A control method for controlling an image forming apparatus,
comprising the steps of:
(a) a first generating step for generating an image signal
representing a predetermined test image having a plurality of tone
levels;
(b) forming the predetermined test image on a recording medium of
the image forming apparatus, based on the image signal;
(c) a first measuring step for measuring density levels of the
predetermined test image formed in the forming step, corresponding
to each of the plurality of tone levels of the image signal;
(d) determining a characteristics of a change of density levels in
the predetermined test image to a change of tone levels in the
image signal, in the image forming apparatus, based on a plurality
of density levels measured in the first measuring step, and making
a conversion data table for converting tone levels of an input
image signal in accordance with the characteristics;
(e) a second generating step for generating an image signal
representing a predetermined test image having a plurality of tone
levels and forming the predetermined test image on the recording
medium of the image forming apparatus based on the image
signal;
(f) transferring the predetermined test image formed in the second
generating step to a recording sheet;
(g) a second step for measuring density levels of the predetermined
test image on the recording sheet corresponding to each of the
plurality of tone levels of the image signal generated in the
second generating step; and
(h) correcting the conversion data table based on the density
levels measured in the second measuring step.
2. The method according to claim 1, wherein in said second
measuring step, the predetermined test image on the recording sheet
is read by an image reader which reads an original.
3. The method according to claim 1, wherein the image forming
apparatus forms a color image by overlaying a plurality of images,
each image having a different color component, and in first
generating step, the image signal is generated corresponding to
each of a plurality of color components, in the determining step,
the conversion data table is made for each of the plurality of
color components.
4. The method according to claim 3, wherein in said second
generating step, the predetermined test image having a color
component designated by a manual operation is formed on the
recording medium, and in the correcting step, data in the
conversion data table corresponding to the color component
designated by the manual operation is corrected.
5. The method according to claim 3, wherein in the second
generating step, the predetermined test image on the recording
medium is formed in correspondence with each of the plurality of
color components, and in the correcting step, data in the
conversion data table is corrected in correspondence with each of
the plurality of color components.
6. The method according to claim 1, wherein the conversion data
table is stored into a non-volatile memory.
7. The method according to claim 1, wherein in the determining
step, the conversion data table is made to change density levels of
an output image linearly to a change of density level of an input
image.
8. An image forming apparatus, comprising:
generating means for generating an image signal representing a
predetermined test image having a plurality of tone levels;
image forming means for forming the predetermined test image on a
recording medium based on the image signal;
first measuring means for measuring density levels of the
predetermined test image formed by said image forming means,
corresponding to each of the plurality of tone levels of the image
signal;
control means for determining a characteristics of a change of
density levels in the predetermined test image to a change of tone
levels in the image signal, in said image forming means, based on a
plurality of density levels measured by said first measuring means,
and for making a conversion data table for converting tone levels
of an input image signal in accordance with the
characteristics;
designating means for generating an instruction for designating a
correction of the conversion data table made by said control
means;
transfer means for transferring an image formed on the recording
medium to a recording sheet; and
second measuring means for measuring density levels of the image
recorded on the recording sheet;
wherein said control means controls said generating means, said
image forming means, and said transfer means to record an image
having a plurality of tone levels on a recording sheet, and causes
said second measuring means to measure density levels of the image
recorded on the recording sheet corresponding to each of the
plurality of tone levels, and corrects the conversion data table
based on the density levels.
9. The apparatus according to claim 8, wherein said second
measuring means causes a reader which reads an original to read the
image on the recording sheet and measures the density levels of the
image read by the reader.
10. The apparatus according to claim 8, wherein said image forming
means forms an image having a plurality of color components and
said control means makes the conversion data table for each of the
plurality of color components.
11. The apparatus according to claim 10, wherein said control means
corrects the conversion table having a color component designated
by an operator.
12. The apparatus according to claim 8, wherein the conversion
table is stored in a non-volatile memory.
13. The apparatus according to claim 8, wherein said control means
makes the conversion data table to change density levels of an
output image linearly to a change of density level of an input
image.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus which
forms a test image on a recording medium and measures the density
of the test image, and then determines an image forming condition
based on the measurement result.
2. Description of Related Art
A method for adjusting image processing characteristics in image
forming apparatuses, such as a copying machine or a printer,
includes: starting the image forming apparatus; after warming-up
operation, forming a specific pattern image on an image holding
member (e.g. a photosensitive drum) measuring the density of the
pattern image; and based on a density value, changing an operation
parameter of a circuit such as a .gamma. corrector for determining
an image forming condition, to maintain image quality.
In a case where image forming characteristic is changed due to
change in environmental conditions, again the specific pattern
image is formed on the image holding member. Also, the density of
the formed pattern image is measured again, and the measurement
results is fed back to the circuit for determining the image
forming condition such as the .gamma. corrector. Thus, image
quality can be maintained in accordance with the amount of the
change in the environmental conditions.
However, if the image forming apparatus is used for a long term,
the measurement result of test pattern density on the image holding
member might not correspond with that of an actually-formed image
on a paper. For example, a cleaning blade for cleaning excessive
toner is provided in contact with the photosensitive drum. The
contact state for a long time may roughen the photosensitive drum
surface, and relation between the amount of toner adhered onto the
photosensitive drum and reflected light amount from the
photosensitive drum upon density measurement may change.
Accordingly, in an image forming apparatus used for a long term, if
the image forming condition is determined using a density
conversion parameter based on density data from initial
measurement, image of corresponding density to the image data
cannot be obtained.
SUMMARY OF THE INVENTION
The present invention has as its object to provide an image forming
apparatus in which the above drawback is eliminated.
Another object of the present invention is to provide an image
forming method and apparatus which prevent image quality from
deterioration due to degradation of parts in long use.
Further object of the present invention is to provide an image
forming apparatus which compensates transition of the relation
between the density of image formed on a recording medium and
result of measurement of the image density on an image holding
member so as to always obtain a high-quality image.
Other objects and advantages besides those discussed above shall be
apparent to those skilled in the art from the description of a
preferred embodiment of the invention which follows. In the
description, reference is made to accompanying drawings, which form
a part thereof, and which illustrate an example of the invention.
Such example, however, is not exhaustive of the various embodiments
of the invention, and therefore reference is made to the claims
which follow the description for determining the scope of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate embodiments of the
invention and, together with the description, serve to explain the
principles of the invention.
FIG. 1 is a block diagram showing the configuration of a copying
machine according to a first embodiment of the present
invention;
FIG. 2 is a sectional view of a printer of the copying machine in
the first embodiment;
FIG. 3 is a block diagram showing the construction of an image
signal processor for processing an electric signal from a CCD of a
reader in the first embodiment;
FIG. 4 is a four-quadrant chart showing the relation between in an
original image density (image data density) and the density of an
actually-printed image;
FIG. 5 is a block diagram showing the construction of a circuit for
processing a signal from a photosensor of a drum surface unit;
FIG. 6 is a line chart showing a yellow toner spectral
characteristic;
FIG. 7 is a line chart showing a magenta toner spectral
characteristic;
FIG. 8 is a line chart showing a cyan toner spectral
characteristic;
FIG. 9 is a line chart showing a black toner spectral
characteristic (one-component magnetism);
FIG. 10 is a line chart showing the relation between an laser
output and the density on an photosensitive drum holding toner
image formed by the laser;
FIG. 11 is a line chart showing conversion characteristics for
converting a photosensor signal to a density signal with respect to
each color;
FIG. 12 is a flowchart showing tone-control processing upon
switching-on of the copying machine in the first embodiment;
FIG. 13 illustrates detection of the density of a patch pattern
formed on the photosensitive drum by the photosensor;
FIG. 14 is a line chart showing change between characteristic of
reflected light amount from the photosensitive drum and that of
output image data density;
FIG. 15 is a flowchart showing updating processing of conversion
table data and LUT data in a density converter according to the
first embodiment of the present invention;
FIG. 16 illustrates a patch-pattern of tone levels in a designated
color;
FIG. 17 is a flowchart showing updating processing of conversion
table data and LUT data in a density converter according to a
second embodiment of the present invention;
FIG. 18 illustrates a patch pattern of tone levels in all colors
according to the second embodiment; and
FIG. 19 is a sectional view of a monochromatic copying machine
according to another embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described in
detail in accordance with the accompanying drawings.
FIRST EMBODIMENT
FIG. 1 is a block diagram showing a color copying machine according
to the first embodiment.
In FIG. 1, reference numeral 201 denotes a controller for
controlling the overall copying machine. The controller 201
comprises CPU 28, which is, e.g., a microprocessor, ROM 210 in
which control programs for the CPU 28 and various data are stored,
and RAM 212 used as a work area for the CPU 28. Test pattern data
to be described later is stored in a test pattern area 211 of the
ROM 210. Numeral 202 denotes an original image reader having a CCD
sensor 21. The reader 202 reads an original image and outputs a
read image signal to the controller 201. The image signal from the
CCD 21 is corrected using a look-up table (LUT) 25 to be described
later and outputted to a printer 100. The printer 100 comprises.
e.g., a laser-beam printer as shown in FIG. 2. Numeral 115 denotes
a sensor unit for examining the surface of photosensitive drum 106.
The sensor unit 115 comprises an LED 10 and a photosensor 9.
Density converter 42 of the controller 201 performs conversion on a
signal from the photosensor 9 and inputs the converted signal into
the CPU 28 for performing control based on this signal. The above
construction will be described in detail with reference to the
subsequent drawings.
FIG. 2 is a sectional view of the structure of the laser-beam
printer (LBP) of the printer 100.
In FIG. 2, the printer 100 forms an image based on an image signal
from the reader 202 on a recording sheet as a recording medium.
Numeral 300 denotes an operation panel on which various operation
switches, LED's and display and the like are provided; and 101, a
printer control unit for controlling the overall printer 100 and
analyzing information such as character information from a host
computer. The printer control unit 101 converts the image signal
into a semiconductor laser driving signal, and outputs the signal
to a laser driver 102.
The laser driver 102 drives a semiconductor laser 103 by on-off
switching the semiconductor laser in accordance with the input
image signal. Laser light 104 scans on the photosensitive drum 106
in a right-and-left direction by rotation of a polygon mirror 105,
thus forming a latent image on the photosensitive drum 106. As
shown in FIG. 2, the drum 106 turns in a direction represented by
an arrow. The latent image is developed by rotating a developer 112
in respective colors (FIG. 2 shows yellow toner development). 107
denotes a developing unit.
On the other hand, the recording sheet is rolled around a transfer
drum 113. The drum 113 turns four times for four colors, and the
rotating developer 112 develops images in order Y (yellow).fwdarw.M
(magenta).fwdarw.C (cyan).fwdarw.Bk (black) each time the drum 113
turns, thus the four color images are transferred onto the
recording sheet. Thereafter, the recording sheet is removed from
the transfer drum 113. Fixing rollers 114 fix the image on the
recording sheet, and the color print image is completed. The
recording sheets are cut sheets set in a paper cassette 108
attached to the printer 100. Paper feeding roller 109 and paper
conveying rollers 110 and 111 introduce the recording sheet into
the printer 100, and supply the sheet to the transfer drum 113. The
drum surface sensor unit 115 comprises the LED 10 which emits near
infrared radiation (main wavelength: 960 nm) to irradiate the
surface of the photosensitive drum 106, and the photosensor 9 which
detects reflected light from the photosensitive drum 106.
FIG. 3 is a block diagram showing the construction of an image
signal processor for obtaining a pattern image of tone levels. The
image signal processor is provided in the controller 201.
When the CCD 21 of the reader 202 reads an original image and
outputs an analog luminance signal, an A/D converter 22 converts
the analog luminance signal to a digital luminance signal. Shading
corrector 23 inputs the digital luminance signal and corrects the
fluctuation of the digital luminance signal came from the
unevenness of the sensitivity of sensors of the CCD 21. LOG
converter 24 performs LOG-conversion to the shading-corrected
luminance signal. The LOG-converted signal is converted using a
look-up table (LUT) 25 so that an output image density processed in
accordance with the initially-set .gamma. characteristic of the
printer 100 will correspond to the original image density.
Pulse-width modulator 26 performs pulse-width modulation upon the
converted image signal, and outputs the signal to the laser driver
102. The laser driver 102 drives the semiconductor laser 103 in
accordance with the pulse-width-modulated signal. Pattern generator
29 generates a pattern of various tone levels to be described
later.
In the present embodiment, pulse-width modulation is employed as
tone-representation. Laser light which is pulse-width modulated
scans on the photosensitive drum 106 to form a latent image in
which one pixel width depends upon the density of the pixel.
Through development, transfer and fixing processes, a half-tone
image can be obtained.
FIG. 4 is a four-quadrant chart showing density reproducing
characteristics of original image.
In FIG. 4, the first quadrant (upper right) shows the
characteristic of the reader 202 which outputs an original image
density as a density signal; the second quadrant (lower right), the
characteristic of the LUT 25 which converts the density signal to a
laser output signal; the third quadrant (lower left), recording
characteristic of the printer 100 which converts the laser output
signal to a recording density; and the fourth quadrant (upper
left), as the relation between the original image density and the
density of a printed image in the copying machine of the present
embodiment. Regarding the number of tone-levels, as an eight-bit
digital signal is employed, image data has two-hundred and
fifty-six tone levels.
In the fourth quadrant, to obtain a linear tone characteristic as
shown in FIG. 4, a curvature of the printer characteristic in the
third quadrant is corrected with the characteristic of the LUT 25
in the second quadrant. The LUT data of the LUT 25 is generated
from calculation to be described later.
In the copying machine of the present embodiment, a predetermined
test pattern is stored in the test pattern area 211 of the ROM 210
in advance, and based on this pattern, a test pattern image is
formed.
FIG. 5 is a block diagram showing a processor for processing a
signal from the photosensor 9 of the drum surface sensor unit 115.
The processor is provided in the controller 201.
The photosensor 9 receives the near infrared radiation, emitted
from the LED 10 and reflected from the surface of the
photosensitive drum 106, and converts the near infrared radiation
to an electric signal. The A/D converter 41 converts the electric
signal to a digital signal. That is, 0-5 V output voltage of the
photosensor 9 is converted to 0-255 levels digital signal. Further,
the density converter 42 converts the digital signal to a density
signal using a conversion table 42a, and inputs the density signal
into the CPU 28. Color toner employed in the copying machine of the
present embodiment comprises separately arranged yellow, magenta
and cyan toners, each having styrene copolymerized resin as
binder.
FIGS. 6 to 8 show spectral characteristics of the respective
yellow, magenta and cyan toners. As it is apparent from these
figures, in each color, the reflectance to the near infrared
radiation (960 nm) is over 80%. In image formation using these
color toners, two-component developing method which is advantageous
for attaining color purity and transparency is employed.
On the other hand, black toner is one-component magnetism toner
which is for monochromatic copying and is effective to reduce
running cost. FIG. 9 shows the spectral characteristic of the black
toner. As apparent from FIG. 9, the reflectance to the
near-infrared radiation (960 nm) is about 10%. In this embodiment,
the black toner is developed by the one-component jumping method.
Note that this developing method can be applied to two-component
black toner.
The photosensitive drum 106 is an OPC (Organic Photo Conductor)
drum having about 40% reflectance to the near-infrared radiation
(960 nm). The drum 106 may be an amorphous silicon drum.
FIG. 10 shows the relation between an output image density and the
output of the photosensor 9 upon stepwisely changing the density of
respective color images formed on the photosensitive drum 106. In
FIG. 10, when no toner is adhered onto the drum 106, the
photosensor output is 2.5 V, i.e., one-hundred and twenty-eight
level.
As it is understood from FIG. 10, as laser output signal level
increases, area covering rates (image density) of the respective
yellow, magenta and cyan color toners raise, the intensity of
reflection light from the photosensitive drum 106 increases, and
the photosensor 9 output becomes greater. On the other hand, as the
area covering rate (image density) of black toner raises, the
reflectance from the black toner becomes lower, and as a result,
the photosensor 9 output decreases.
The density conversion table 42a has data characteristic for
converting the photosensor 9 output to a density signal in each
color, as shown in FIG. 11, thus enabling to detect the density of
an original image with high precision.
Next, density conversion characteristic setting processing upon
switching-on of the copying machine in the present embodiment will
be described with reference to a flowchart of FIG. 12. It should be
noted that the control program for this processing is stored in the
ROM 210.
First, in step S1, the power of the copying machine is turned on,
and in step S2, whether or not the temperature of the fixing roller
114 is equal to or lower than 150.degree. C. is examined by a
thermistor (not shown). If YES (lower than 150.degree. C.), the
tone control is performed in step S3, while if NO (over than
150.degree. C.), message "COPYING POSSIBLE" is displayed on the
display of the operation panel 300 in step S10.
In step S3, the process waits until it is confirmed that the
temperature of the fixing roller 114 has increased to a
predetermined value (e.g. 150.degree. C.) and the temperature of
the semiconductor laser 103 has increased to a predetermined value,
and the machine is in stand-by status. In step S4, the output
signal level of the laser 103 is set to the maximum "255", and a
toner image for a patch test pattern in this density is formed on
the photosensitive drum 106. Then, the reflectance from the drum
surface is obtained based on the photosensor 9 output, and in step
S5, the photosensor 9 output is converted to an image density in
accordance with the conversion characteristic as shown in FIG.
11.
Next, the difference between the obtained image density and a set
maximum density of the copying machine is examined. In accordance
with the difference, contrast potential of a bright-portion of a
latent image to a dark-portion of the latent image to be formed on
the photosensitive drum 106 is calculated, and the obtained
potential is set in step S6.
In step S7, a pattern of a color, e.g., yellow toner, of specific
density levels is continuously formed around the photosensitive
drum 106 as shown in FIG. 13. In this embodiment, a test pattern of
sixteen density levels (16th, 32th, 48th, 64th, 80th, 96th, 112th,
128th, 144th, 160th, 176th, 192th, 208th, 244th, 240th, 255th
levels in this embodiment) is formed. The reflection amount of the
test pattern is measured at an appropriate timing by the LED 10 and
the photosensor 9. In step S8, the photosensor output is converted
to an image density in accordance with the conversion
characteristic as shown in FIG. 11. Thus, the relation between the
image density and the laser output value, i.e., the printer
characteristic shown in the third quadrant in FIG. 4, can be
exactly obtained from the reflection amount of the test pattern
formed on the photosensitive drum 106, without forming a print
image on a recording sheet.
In step S9, data for the LUT 25 for correcting image data based on
the printer characteristic obtained in step S8 is calculated. The
LUT data can be easily obtained from the printer characteristic,
i.e., the LUT data can be calculated by reversing input-output
relation of the printer characteristic (by obtaining a symmetrical
data with the y-axis as the central axis as shown in FIG. 4). The
above control is repeated for the respective colors. Thereafter,
the message "COPYING POSSIBLE" is displayed on the operation panel
300 in step S10, and the machine becomes in stand-by status.
In actual copying operation, by performing density conversion based
on the obtained LUT 25 data, tonality having a linear
characteristic with respect to the semiconductor laser 103 can be
obtained.
Next, a case where the copying machine has been used for a long
term, and the density of a pattern formed on the photosensitive
drum and that of an actually-printed image no longer correspond
with each other, will be described below. For example, if a
cleaning blade for removing untransferred toner is in contact with
the photosensitive drum 106 for a long period, scattered light
component of the photosensitive drum 106 increases. This makes the
relation between the photosensor 9 output and an image density
different from that in an initial status.
FIG. 14 shows the relation between the sensor 9 output and the
density of a pattern image formed on the photosensitive drum 106
with yellow toner. Numeral 140 denotes an initial sensor output
characteristic; and 141, a sensor output characteristic after
copying for ten-thousand sheets. This shows a tendency that the
long-term utilization makes an image density detected by the
photosensor 9 lower than that in the initial status.
FIG. 15 is a flowchart showing the process of updating the data of
the conversion table 42a and the LUT 25 in the copying machine of
the present embodiment. The control program for this processing is
stored in the ROM 210.
In step S21, a color of the conversion table to be updated is
designated from the operation panel 300, and a control switch for
instructing start of the processing is turned on. In step S22, a
pattern of sixteen tone levels in the designated color (See FIG.
16) based on the test pattern stored in the ROM 210 is outputted by
the pattern generator 29. The pattern of sixteen tone levels in the
designated color is transferred onto the recording sheet.
In step S23, the operator places the recording sheet on a platen of
the reader 202, as a print sample on which the pattern image is
formed, and inputs a reading instruction from the operation panel
300. The pattern image signal read by the CCD 21 is A/D converted,
shading-corrected, LOG-converted, and converted to a density data.
In step S24, data of the conversion table 42a (as shown in FIG. 5)
for the designated color is generated based on the relation between
the density data and the laser output density upon test pattern
outputting. To form the conversion table 42a data, the a linear
interpolation may be adopted to generate data between sixteen-point
data. Preferably, to improve precision, a non-linear interpolation
or non-linear approximation may be applied. In step S25, the data
of conversion table 42a is updated.
Next, in step S26, based on the relation between the density data
and the laser output density, obtained in step S24, the LUT 25 data
is calculated and the obtained table data is written into the LUT
25.
Thus, the embodiment enables even a copying machine used for a long
term to form an image of excellent tonality by periodically
performing the above processing.
SECOND EMBODIMENT
In the first embodiment, a pattern image in a designated single
color is formed, and the conversion table data is updated based on
the relation between the recording density and the output density.
However, as the abovementioned problem, i.e., an original image
density and the density of an actually-printed image do not
correspond with each other, is likely to occur in all the color
toners, the second embodiment is directed to correction to all
colors, such as yellow, magenta, cyan and black.
FIG. 17 shows the processing according to the second embodiment.
The control program for this processing is stored in the ROM 210.
Note that hardware construction of the second embodiment is
identical to that of the first embodiment.
In step S31, the control switch on the operation panel 300 is
turned on, similarly to step S21 in FIG. 15. Patterns respectively
of sixteen tone levels in yellow, magenta, cyan and black as shown
in FIG. 18 are sequentially outputted by the pattern generator 29
in step S22. Toner images of the patterns are sequentially formed
on the photosensitive drum 106, and the respective color images are
sequentially transferred on the recording sheet. Next, in step S33,
the operator places the recording sheet on the platen of the reader
202 as a print sample, and inputs a reading instruction. Similarly
to step S23, the pattern image is read by the CCD 21, LOG-converted
and converted to a density data. In step S34, the relation between
the density data (of the pattern image on the sheet) and the laser
output density is obtained. The conversion table 42a data
corresponding to the respective colors are obtained in a similar
manner as that in step S25 in FIG. 15. In step S35, the conversion
table 42a data are updated. Similarly to step S25, in step S35, the
linear interpolation is performed to generate data between the
sixteen-point data, however, preferably, non-linear interpolation
or non-linear approximation may be applied to improve precision. In
step S36, the data for all colors of the LUT 25 are calculated
based on the relation between the density data and the laser output
density, and the obtained data is set in the LUT 25.
Thus, the second embodiment enables to obtain an image of excellent
tonality and good color balance.
It should be noted that the embodiments are described as a
full-color digital copying machine. However, the present invention
is not limited to the digital copying machine, but is applicable to
a monochromatic digital copying machine.
FIG. 19 is a sectional view of a monochromatic digital copying
machine according to another embodiment. In FIG. 19, parts
corresponding to those in the aforementioned embodiments have the
same reference numerals.
In FIG. 19, reference numeral 190 denotes a light source for
irradiating an original; and 191, a lens for focusing reflection
light from the original. The CCD 21 reads the original, and the A/D
converter 22 converts an image signal to a digital signal and
outputs the digital signal to CPU 195. Numeral 192 denotes an
original cover; and 193, a platen. Similarly to the aforementioned
embodiments, the photosensor 9 detects the density of an image on
the photosensitive drum 106, and the A/D converter 41 converts the
density signal to a digital signal and outputs the digital signal
to the CPU 195. Numeral 197 denotes a developer; and 198, a
recording sheet.
This copying machine also obtains an image of excellent tonality
for a long period by updating the data of density conversion table
42a and the LUT 25 in accordance with the flowchart in FIG. 15.
The present invention can be applied to a system in which a reader
and a printer are separated, or to an apparatus having a reader and
printer as an integrated unit. Furthermore, the invention is
applicable also to a case where the object of the invention is
attained by supplying a program to a system or apparatus.
As many apparently widely different embodiments of the present
invention can be made without departing from the spirit and scope
thereof, it is to be understood that the invention is not limited
to the specific embodiments thereof except as defined in the
appended claims.
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